The invention discloses an explosion suppressant and a preparation method thereof. The explosion suppressant is prepared from raw materials in percentage by mass as follows: 15%-18% of an aluminum alloy matrix, 20%-25% of ammonium polyphosphate, 3%-5% of hard polyurethane foaming plastic, 10%-15% of diatomite, 5%-15% of white carbon black, 5%-10% of talc powder, 8%-12% of aramid pulp and the balance of boron carbide particles, wherein the aluminum alloy matrix is prepared from components in percentage by weight as follows: 0.8%-1.5% of manganese, 2.0%-2.5% of zinc, 0.2%-0.5% of silicon, 0.8%-1.0% of scandium, 0.5%-0.8% of zirconium, 1.8%-2.5% of titanium and the balance of aluminum. According to the explosion suppressant, crystals in the aluminum alloy matrix are changed and uniform, so that the rigidity and the extensibility are improved, and the explosion suppressant has great regarding and heat absorbing functions; under the joint function of the constituents, the explosion occurrence time can be effectively delayed, the maximum pressure during an explosion and the pressure rising speed can be reduced, and explosion occurrence and spreading are inhibited.